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[Display omitted] • Fluorescent phosphorous doped carbon quantum dots from banana stem were synthesized by a facile hydrothermal method. • P-CQDs exhibited excellent water solubility, fluorescent stability and superb biocompatibility. • The P-CQD have been employed for fluorescence-based imaging of biological samples. In this work, a simple hydrothermal process was employed to create phosphorous-doped fluorescent carbon quantum dots (P-CQD) from biomass banana stems. The formation of the P-CQDs and the surface functional group was confirmed through a variety of characterization methods, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), (transmission electron microscopy) TEM, (field emission scanning electron microscopy) FESEM, Fourier transform infrared spectroscopy (FTIR), and (ultraviolet–visible) UV–vis spectroscopy. The quantum yield of the synthesized P-CQDs was found to be 15 %. The P-CQDs showed excitation-dependent photoluminescence (PL) emission behaviour possessing a blue fluorescence under UV light. The P-CQDs was utilized for in vitro cytotoxicity effect on Muscle (L6) and Kidney cells (HEK293). The minimum cell viability for the P-CQD was 96.24 %, while the maximum cell viability was approximately 100 % at a concentration of 400 μg/mL. This study suggests that P-CQDs were non-toxic and could be employed for fluorescence-based cell imaging. [ABSTRACT FROM AUTHOR]

A green and facile method for the synthesis of carbon dots (CDs) have been developed using lignocellulosic biomass (banana stem) and phosphoric acid to construct fluorescent sensor for Cr(VI) detection. The effects of phosphoric acid and temperature on the fluorescence behavior of carbon dots have been explored elaborately. The optical and structural properties of the CDs were determined by different characterization techniques. The prepared CDs display excellent fluorescence properties with intense bright blue emission spectra around 447 nm at an excitation wavelength of 350 nm. The CDs possessing the highest quantum yield (15.1%) have an immense sensing potential to detect Cr(VI) in linear detection range (10–30 μM) with detection limit of 2.4 μM. Furthermore, the CDs have been applied to quantitatively detect Cr(VI) in real water samples. Theoretical studies based on DFT and TDDFT calculations suggested the detection pathway of Cr(VI) occurs via photoinduced electron transfer (PET) which furthur supports the experimental studies. [Display omitted] • A green synthesis route to produce carbon dots (CDs) from waste banana stem. • A fluorometric method was used for sensing of Cr(VI) at emission wavelength 447 nm. • The CDs shows a detection limit of 2.4 μM. [ABSTRACT FROM AUTHOR]